Re: [PATCH v2] rtc: zynqmp: Enable crystal oscillator when setting time

[sashiko-bot@kernel.org]

> The RTC_OSC_EN macro was defined when the driver was originally
> introduced, but was never asserted by the driver. On cold boots, after
> battery exhaustion, or on platforms where firmware does not configure
> RTC_CTRL, the oscillator remains disabled and the counter never ticks.
> 
> Unconditionally enabling the oscillator during driver initialization
> would cause the RTC to free-run from an uninitialized or stale counter
> value, reporting an untrusted time to userspace. Instead, keep the
> oscillator disabled until a valid time is programmed: guard
> xlnx_rtc_read_time() on RTC_OSC_EN and return -EINVAL when it is not
> set, and assert RTC_OSC_EN in xlnx_rtc_set_time() once valid time is
> programmed so the RTC can free-run.
> 
> Per the Zynq UltraScale+ TRM (UG1085), bit 24 (OSC_CNTRL) is a static
> level enable for the crystal inverter rather than an edge-triggered reset;
> asserting it from set_time() is non-destructive and will not glitch an
> already-running oscillator.
> 
> Tested on Zynq UltraScale+ hardware, confirming that read_time returns
> -EINVAL while the oscillator is disabled, and advances reliably after
> setting time.
> 
> Fixes: 11143c19eb57 ("rtc: add xilinx zynqmp rtc driver")
> Cc: stable@vger.kernel.org
> Signed-off-by: Daniel Viaño <danividanivi@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260925052015.22019-1-danividanivi@gmail.com?part=1